UPWELLING AND THE PRODUCTION OF FISH
303
taken at thc surface, at 50 m and at 100 m (Hentschel, 1033). Kamshilov’s ( 195 1) formula converting length to weights for copepodites
(0.6-1.0 mm) and nauplii (0.08-0.10 mm) has been used. This procedure yields results which are comparable with those from other upwelling areas.
Most of the observations of zooplankton stock are expressed as
ml/l 000 m3 displacement volume (in American usage) or mg/m3 wet
weight (in Russian usage), and in this paper they are treated as being
the same. As the nets are hauled from specified depths the quantity per
cubic metre can be readily converted to a quantity beneath a square
metre. In the upwelling areas the nets have been hauled usually from
about 200 m, which is approximatcly the depth of the upwelled water.
It is possible that some animals, for example euphausids, rise from
deeper water into the upper 200 m at night, in which case the stock is
underestimated to some extent.
An upwelling area might be 800 km in length by 200 km in width
(in the biological sense) ; a part of it contributes to a current flowing towards the equator at about 20 km/day (Wooster and Reid, 1963), which
means that water passes through the area in about 40 days. There is
thus an input of zooplankton from the poleward end, which has been
generated in the divergences further away. Very roughly, it takes one
zooplankton generation for water and zooplankton to be drifted across
the length of an upwelling area. Any mature copepod reaching an
upwelling area would ensure a high survival rate for its offspring in the
high algal production there. But plankton animals are probably also
generated within the water which has risen from below, and because of
the mixture between the two potential sources it may be idle to distinguish between them. We may consider the production of zooplankton
to be autonomous within the upwelling area only, because there may be
one generation within the drift time across the area. The upwelling
scason may last for many months in some areas and the production of
zooplankton is given by the average standing stock as ml/m2, multiplied
by the number of generations during the upwelling season. This is a
fair estimate if the generations are discontinuous, as they are in temperate waters, but if breeding goes on all the time, the measure of a
generation for production purposes is not the interval between the
appearance of mature adults, but is something less, depending upon the
mortality. From the structure of the production cycle in thc upwelling
area, such an effect might be expected, but no evidence is yet available
on the possible mortality rate.
Marshall and Orr (1956) give thc duration of copcpodite stages as a
proportion of the duration of oopepoclito stagr I. McLaren (1 965) has
303
taken at thc surface, at 50 m and at 100 m (Hentschel, 1033). Kamshilov’s ( 195 1) formula converting length to weights for copepodites
(0.6-1.0 mm) and nauplii (0.08-0.10 mm) has been used. This procedure yields results which are comparable with those from other upwelling areas.
Most of the observations of zooplankton stock are expressed as
ml/l 000 m3 displacement volume (in American usage) or mg/m3 wet
weight (in Russian usage), and in this paper they are treated as being
the same. As the nets are hauled from specified depths the quantity per
cubic metre can be readily converted to a quantity beneath a square
metre. In the upwelling areas the nets have been hauled usually from
about 200 m, which is approximatcly the depth of the upwelled water.
It is possible that some animals, for example euphausids, rise from
deeper water into the upper 200 m at night, in which case the stock is
underestimated to some extent.
An upwelling area might be 800 km in length by 200 km in width
(in the biological sense) ; a part of it contributes to a current flowing towards the equator at about 20 km/day (Wooster and Reid, 1963), which
means that water passes through the area in about 40 days. There is
thus an input of zooplankton from the poleward end, which has been
generated in the divergences further away. Very roughly, it takes one
zooplankton generation for water and zooplankton to be drifted across
the length of an upwelling area. Any mature copepod reaching an
upwelling area would ensure a high survival rate for its offspring in the
high algal production there. But plankton animals are probably also
generated within the water which has risen from below, and because of
the mixture between the two potential sources it may be idle to distinguish between them. We may consider the production of zooplankton
to be autonomous within the upwelling area only, because there may be
one generation within the drift time across the area. The upwelling
scason may last for many months in some areas and the production of
zooplankton is given by the average standing stock as ml/m2, multiplied
by the number of generations during the upwelling season. This is a
fair estimate if the generations are discontinuous, as they are in temperate waters, but if breeding goes on all the time, the measure of a
generation for production purposes is not the interval between the
appearance of mature adults, but is something less, depending upon the
mortality. From the structure of the production cycle in thc upwelling
area, such an effect might be expected, but no evidence is yet available
on the possible mortality rate.
Marshall and Orr (1956) give thc duration of copcpodite stages as a
proportion of the duration of oopepoclito stagr I. McLaren (1 965) has